The typical architecture of a heating and/or cooling system of a room requires the circulation of a process fluid (typically water) between a heating power and/or cooling power generator (such as a boiler or a refrigerant circuit) and a plurality of terminals (i.e. utilities such as radiators or fan coils). The process fluid moves through a closed circuit due to the prevalence imparted to the fluid by a pump. In particular, the fluid leaves the generator by means of a delivery line, thus transmitting the heating and/or cooling power with which to feed the terminals, and returns to the generator through a return line, once the heating and/or cooling power has been dissipated by the terminals. The delivery line and the return line are connected to a plurality of service lines, each of which includes one or more terminals. The service lines are equipped each with at least one regulating device (such as a valve) whose function is to control and/or interrupt the flow along the service line in which the regulator is installed.
The adjustment of a heating and/or conditioning system makes sure that each terminal is able to dissipate the heating and/or cooling power needed to achieve the desired environmental parameters (typically the temperature and/or humidity set by a user) where the terminal is installed. To ensure that these parameters are met, an adequately accurate control of the power exchanged by a terminal is needed. More in detail, exchanged power must be monitored and if the exchanged power does not allow achieving the desired environmental parameters, the adjustment device intervenes to increase or decrease the flow along the service line and therefore the heating and/or cooling power that can be dissipated by the terminal.
For the assessment of the heating and/or cooling power exchanged by a terminal with the room in which it is installed, measurement of the process fluid flow rate and of the process fluid temperature difference between the terminal delivery and the terminal return are necessary.
To measure flow rate of a fluid along a conduit and, particularly, to measure the flow rate of a fluid along a service line in a heating and/or cooling system of a room (upstream or downstream of a terminal), several technical solutions are known in the prior art which use different technologies.
According to the technical solutions that use ultrasound technology, the working principle of a flow meter is based on the difference of an ultrasonic pulse transit time through a fluid. This pulse, emitted by the meter, provides an output signal directly proportional to the speed of the liquid and thus to the instant flow rate. The technical solutions based on ultrasounds are appreciated for the accuracy of the measurements and for the amplitude of the range of detectable flow rates. However, they have the objective drawbacks of a high cost, excessive footprint and a more difficult integration in retrofits to existing heating and/or cooling systems.
According to the technical solutions that use the technology commonly referred to as “Vortex”, the flow meter is based on the principle of vortex precession, theorized by Von Karman. When a fluid flows and meets a suitable generating fin, alternating vortices are formed, which detach from both sides with opposite direction of rotation. Pressure fluctuations due to the formation of vortices are detected by a sensor and converted into electrical pulses. The vortices are generated regularly within the limits of application of the meter. As a result, the generation frequency of the vortices is directly proportional to the flow rate. The technical solutions based on vortex precession are appreciated for the affordability and compactness of the meters. However, they have the objective drawbacks of a minimum detectable flow rate which is too high (of the order of 30 l/h). In addition, this type of detectors has unsatisfactory accuracy at flow rates below 25% of the measurable range. Therefore, the amplitude of the range of detectable flow rate values with vortex precession meters is greatly reduced.
Finally, according to the technical solutions that use a calibrated orifice (namely, a bottleneck which creates a narrow section where the flow is made to pass), the meter detects the pressure difference between the upstream and downstream of this narrow section. Suitable pressure pick-up lines are placed upstream and downstream of the narrow section, so that the pressure difference across the narrow section can be detected. The pressure differential, the geometric characteristics of the meter, and the knowledge of the fluid allow calculating the flow rate using an appropriate algorithm. The technical solutions based on the differential pressure are appreciated for the affordability and compactness of the meters. However, they have limited amplitude of the range of detectable flow rates which jeopardizes an effective use thereof in heating and/or cooling systems.
That being said, with particular reference to differential pressure meters (which can be used in a heating and/or cooling system, typically in conjunction with a calibrated orifice), the solutions known in the prior art have a number of significant problems.
A first criticality is related to the differential pressure values detectable by the meter. Generally, in fact, differential pressure meters, because of their working principle, are intrinsically characterized by a rather limited detection range, as previously mentioned. In addition to that, some known differential pressure meters have a too limited value of minimum detectable differential pressure.
A second criticality is related to the resolution of the known differential pressure meters. Also such criticality is particularly felt if the differential pressure meter is used for indirect measurements of a flow rate. In fact, in heating and/or cooling systems, in order to obtain fine adjustments of the systems (which allow consequent fine adjustments of the environmental parameters within the rooms served by the systems), it is very useful that the same are provided with the ability to finely vary the flow (for example through ball valves) and consequently with the ability to detect such fine variations.
A third criticality is related to the set up of the known differential pressure meters to be installed along conduits of heating and/or cooling systems. In this regard, in addition to the aspect related to the dimensions and the aspect related to the incidence of the meters on the overall system cost, there are additional critical aspects, related respectively to the poor attitude of the known differential pressure meters to be integrated in the intelligence of the management system that controls a heating and/or cooling system and to the lack of adequate ability to ensure, when installed, the necessary fluid-tightness, thus making the heating and/or cooling system susceptible of flow losses right at the points where the differential pressure meters are installed.